/*
 * Copyright 2012 The Netty Project
 *
 * The Netty Project licenses this file to you under the Apache License,
 * version 2.0 (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at:
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations
 * under the License.
 */
package io.netty.example.echo;

import io.netty.bootstrap.ServerBootstrap;
import io.netty.buffer.PooledByteBufAllocator;
import io.netty.buffer.UnpooledByteBufAllocator;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.ChannelPipeline;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioChannelOption;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.handler.logging.LogLevel;
import io.netty.handler.logging.LoggingHandler;
import io.netty.handler.ssl.SslContext;
import io.netty.handler.ssl.SslContextBuilder;
import io.netty.handler.ssl.util.SelfSignedCertificate;

/**
 * Echoes back any received data from a client.
 */
public final class EchoServer {

    static final boolean SSL = System.getProperty("ssl") != null;
    static final int PORT = Integer.parseInt(System.getProperty("port", "8007"));

    /**
     * Netty 服务端启动流程
     * ● 配置 EventLoopGroup 线程组；
     * ● 配置 Channel 的类型；
     * ● 设置 ServerSocketChannel 对应的 Handler；
     * ● 设置网络监听的端口；
     * ● 设置 SocketChannel 对应的 Handler；
     * ● 配置 Channel 参数。
     *
     * @param args
     * @throws Exception
     */
    public static void main(String[] args) throws Exception {
        // Configure SSL.
        final SslContext sslCtx;
        if (SSL) {
            SelfSignedCertificate ssc = new SelfSignedCertificate();
            sslCtx = SslContextBuilder.forServer(ssc.certificate(), ssc.privateKey()).build();
        } else {
            sslCtx = null;
        }

        // Configure the server.
        // 主 Reactor
        EventLoopGroup bossGroup = new NioEventLoopGroup(1);
        // 从 Reactor
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        final EchoServerHandler serverHandler = new EchoServerHandler();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .option(ChannelOption.SO_BACKLOG, 100)
                    // 两种设置keepalive的方式
                    .childOption(ChannelOption.SO_KEEPALIVE, true)
                    .childOption(NioChannelOption.SO_KEEPALIVE, true)
                    // 切换到池化和非池化的方式之一 UnpooledByteBufAllocator or PooledByteBufAllocator
                    .childOption(ChannelOption.ALLOCATOR, PooledByteBufAllocator.DEFAULT)
                    .handler(new LoggingHandler(LogLevel.INFO)) // // 设置ServerSocketChannel 对应的 Handler
                    // Handler顺序，读保证自上而下，写保证自下而上就行了 读与写之间其实顺序无所谓，但是一般为了好看对称，我们是一组一组写
                    .childHandler(new ChannelInitializer<SocketChannel>() { //  // 设置 SocketChannel 对应的 Handler
                        @Override
                        public void initChannel(SocketChannel ch) throws Exception {
                            ChannelPipeline p = ch.pipeline();
                            if (sslCtx != null) {
                                p.addLast(sslCtx.newHandler(ch.alloc()));
                            }
                            //p.addLast(new LoggingHandler(LogLevel.INFO));
                            p.addLast(serverHandler);
                        }
                    });

            // Start the server.
            // 启动完成才能执行后面的步骤
            // bind() 才是真正进行服务器端口绑定和启动的入口，sync() 表示阻塞等待服务器启动完成
            ChannelFuture f = b.bind(PORT).sync();

            // Wait until the server socket is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down all event loops to terminate all threads.
            // 优雅的关闭Netty
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
